Noise-Canceling Electrostatic Headphones for fMRI

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Electrostatic Transducers

Noise Cancellation



About Me

Wilmot Yeh, 2005 - Project to develop functional high-quality headphones for use in fMRI scanning, to aid studies in music and voice cognition.


Finished an amp board, but still lacking good parts for the power supply. I'm still hesitant about "experimenting" with a heavy transformer too. Because getting a used "energizer" from a company like Stax or Audio-technica (basically an attenuated step-up signal transformer) will cost about the same it would cost to get the necessary parts for the actual power supply (the transformer spec'ed in the plans goes for about $80), so I think at this point, I'm just going to go for that (ebay) so I can start working on testing and the parts that matter (noise-canceling and cabling).

220c Final Presentation



Got some better tools for cutting the aluminum, and am making a couple pairs of new drivers in different sizes. I've also been looking into different ear protectors. There are a few that I feel would work, but I haven't been able to take them apart to play with yet.

Also, got graphite powder to replace the soap, and got a sheet of 30-mil HDPE to replace the old credit cards. Thin HDPE is easily cut with scissors, so different shapes will be easy to make.

Added the Noise Cancellation page. It's not very detailed yet; will be when I get to that part of the project.



Prototype drivers finished:

They're really poorly made, and they'll probably work for about five seconds before messing up. There weren't any big problems, just little annoyances and difficulties (i.e. cutting metal/plastic and keeping it flat....getting the resistive coating to stick...knowing how to tape mylar to the frame so it doesn't come off when I'm not looking...etc).

That said, I do know the associated problems now, and the next sets I make will be nicer. I do need to figure out a better way to cut the aluminum though. It would be great if the mini-hacksaw in the lab had a blade. Maybe I'll go get one.

Notes on drivers: plastic spacers used were peoples' old credit cards, giftcards, and ID cards. Perfect size! But the Stanford IDs actually have a copper wire running behind the magnetic stripe. Weird.

I also cut the stators to be a little larger than the spacers to make sure the more-uneven edges didn't affect the spacing, but only after I finished did I realize that that would create problems with biasing the membrane.

Resistive coating on the mylar is hand soap (which I heard was easier to do than graphite). I originally tried dissolving Ivory soap (flakes left over from a Kimball soap-carving event) but that didn't cover with enough density. Now that I think of it, I may or may not have disposed of the huge bag of soap. I ended up using the weird Airkem stuff from the bathroom. It seems to work, but never really dries. Err...I think I'll stick with graphite next time.

~I will take pictures next time I make drivers.



Added Home/News and Electrostatic Transducers section.

Built first pair of drivers. Look pretty messy but should work. Waiting for part for the amplifier.